96 



of the strings in the tubes was very irregular, and that none of the 

 eggs revolved in the same plane for a single revolution, so that the 

 constant action of the centrifugal force was excluded. 



Results. 



The eggs developed normally and produced normal embryos. It 

 was noticeable that those on the wheel developed faster than those 

 outside. This does not seem to have been due to any difference in 

 the temperature, but to the agitation of the eggs themselves. Such 

 an effect has been claimed by Meltzer f03) to take place in the sea- 

 urchins egg when kept under conditions in which a continuous jarring 

 was present. I tested this point also with two lots of frog's eggs, and 

 found in one case that the cleavage began sooner in the eggs in the 

 tubes on the wheel than in check-eggs outside, also in tubes. In an- 

 other case the eggs were in the late segmentation stage when put on 

 the wheel. In these the dorsal lip of the blastopore appeared sooner 

 in the eggs on the wheel. In both cases, however, the eggs on the 

 wheel soon died. This did not happen in the toad's eggs, because 

 either the eggs are more resistant or better protected, or because the 

 bubbles of air produced a more marked effect (as seemed in fact to 

 be the case) on the larger and more solid bunches of the frog's eggs. 

 The effect produced was very different from that of a centrifugal force, 

 with whose action I am perfectly familiar, and did not produce ab- 

 normal development, but killed the eggs outright. 



Amongst the toad's eggs only one spina bifida embryo appeared, 

 but these also are found not uncommonly in strings under slightly 

 abnormal conditions. Furthermore this type of development is by no 

 means characteristic of centrifugalized eggs, as Moszkowski appears 

 to believe, but can be produced by a large number of unfavorable 

 conditions. It does not follow necessarily that because he found such 

 embryos amongst eggs whirled in water these must have been centri- 

 fugalized, although such embryos may be produced in this, as well as 

 in many other ways. 



From these results, as well as from those of my previous ex- 

 periments, I conclude, that, for the toad, normal embryos may develop 

 when the constant action of gravity and of a centrifugal force are both 

 excluded. 



Bryn Mawr, April 21, 1904. 



